The present invention relates to gas-fired radiant heaters commonly employed in large industrial ovens, and more particularly to an improved radiant heater having a partially compartmentalized fuel distribution system for more uniform heat radiation throughout extended heater lengths and a specially configured air jacket for directing the flow of cooling air within and about the heater structure.
In industrial process heating applications, gas-fired, infra-red heaters are commonly employed in ovens for heating or drying webs of large surface areas. The webs are typically moved through the ovens in proximity to and across the radiant face of the heater which generally comprises a plurality of porous refractory panels mounted upon associated supporting structure. Through the panels a gaseous combustible fuel mixture is passed and the mixture is ignited on the face of the panels causing them to become incandescent and generate infra-red radiation that effectively heats and dries the moving webs.
Extremely high temperatures are achieved as the fuel mixture ignites on the face of the panels. Although most of this heat energy is directed toward the web, a significant portion of it raises the temperature of the supporting structure to an elevated level at which distortion of the supporting structure may occur with accompanying damage to the panels as well as the structure. Such distortion significantly affects the heating and drying of webs and typically requires a shut-down of the operation and the costly repair or replacement of the heaters prior to resumption of normal processing. While current gas-fired, infra-red heaters have generally provided for the circulation of cooling air within and about their supporting structure to reduce its temperature and the consequent risk of distortion, there still remains a need for a more efficient means of cooling the support structure without adversely affecting the radiant heat field generated by the refractory panels and without diminishing the amount of heat applied to the moving web.
Another area of major concern in the effective operation of these infra-red heaters is the even distribution of the fuel mixture along extended lengths so that a substantially uniform incandescence may be maintained along the surfaces of the refractory panels. Generally required in order to properly heat the very large surface areas of the webs, relatively long heaters of 80 inches or more are commonly employed, and an uneven distribution of fuel mixture throughout these extended lengths will result in "cold spots" along the panels and gaps in the radiant heat field applied to the webs. Existing infra-red heaters, particularly their supporting structures, are fabricated from expensive cast iron parts extremely difficult and costly to produce in comparatively long sections. As a result, short cast iron sections, typically of no more than 12 inches, are bolted or otherwise joined together to form a row of heaters of a desired length. While such multiple-sectioned structures have generally provided effective infra-red heat radiation, they can be a cause of "cold spots" and gaps in the radiant heat field, particularly where the sections are joined, and otherwise, remain very expensive and difficult to fabricate.